The present invention relates to a laser exposure unit, and more particularly to a laser exposure unit wherein laser beams of at least two different wavelengths or more scan a recording medium to expose a color image for formation thereof.
As a laser exposure unit to expose a color image for formation thereof, there have been known a unit wherein gas lasers (an argon laser, a helium neon laser and others) for three wavelengths corresponding to B (blue), G (green) and R (red) and an audio-optical modulation element (hereinafter referred to as AOM) are used in combination and a unit having the structure wherein semiconductor lasers for three wavelengths are subjected to direct modulation (internal modulation).
However, an argon laser which is frequently used especially as B light source among gas lasers has had problems that a unit is big in size and is high in cost.
Further, in modulation by means of a conventional AOM, a laser beam emitted from a gas laser has been caused to enter AOM directly. In this case, an exposure speed is restricted by a modulation speed of AOM, which has made it impossible for the exposure speed to be enhanced sufficiently.
On the other hand, if light-sensitive materials sensitive to red wavelength or longer wavelength are used for three layers for C (cyan), M (magenta) and Y (yellow), it is possible to use a relatively inexpensive semiconductor laser for all light sources. However, the light-sensitive material having the aforesaid characteristics is hard to be designed, manufactured and preserved, a price of such light-sensitive material itself is high, which has been a problem. In addition, three wavelengths are close together due to the use of red wavelength and longer wavelength, causing a possibility of occurrence of an interference of adjoining wavelengths, which has been a problem.
The invention has been achieved in view of the problems mentioned above, and its first object is to provide a laser exposure unit which is compact in size and low in cost and which is further capable of exposing a color image stably at high speed.
Next, problems which are related to plural laser beams and are to be solved by the invention will be described as follows.
In an image recording apparatus having therein a light source section where plural laser diodes with the same wavelength are lined up, a beam lining up optical system which lines up laser beams emitted from the plural laser diodes on recording material in the sub-scanning direction, and a moving means which moves the laser beams emitted from the plural laser diodes and the recording material relatively in the main scanning direction, adjustment of intensity of a laser beam has been conducted by controlling an electric current which flows through a laser diode.
However, in the image recording apparatus stated above, both of adjustment to make all laser beams to be in the same intensity and adjustment of exposure intensity for all laser beams emitted from plural laser diodes need to be conducted by controlling an electric current which flows through a laser diode. Though the adjustment to make all laser beams to be in the same intensity does not need to be conducted frequently, shifting of exposure intensity for all laser beans emitted from the plural laser diodes needs to be conducted surely when changing tone reproduction for outputted images and when changing a recording material, which requires frequent adjustment.
However, an electric current flowing through a laser diode and an amount of emitted light are not in a proportional relation, and the relation between an electric current and an amount of emitted light varies depending on each laser diode and the change of the relation is different depending on the passage of time. Therefore, a measuring means which measures beam intensity of each laser beam emitted from each of plural laser diodes has been required to be provided, and it has been necessary to adjust frequently an electric current that flows though each laser diode of plural laser diodes depending on beam intensity of each laser beam measured by the measuring means, when changing tone reproduction of outputted images and changing recording materials, which has been time-consuming.
It has been common that beam intensity of a laser beam from each laser diode is measured by an optical system, and thereby an electric current which flows through each laser diode of plural laser diodes is adjusted.
However, the foregoing has been effective only for adjustment for variation in beam intensity caused by variation of intensity of luminescence of laser diode with the passage of time, and it has been impossible to adjust variation of beam intensity caused by a change in an optical axis.
In the conventional unit, it has been necessary to cause a recording position of a laser beam from each laser diode to agree with the main scanning direction so that the recording position on a recording material may not be deviated. Therefore, accurate adjustment has been necessary for each unit before its installation or after usage thereof for a certain period of time.
The second object of the invention is to solve the problems related to plural beans and thereby to attain the following items. Shifting of exposure intensity for all laser beams emitted from plural laser diodes in the case of changing tone reproduction for outputted images required to be conducted frequently and changing recording materials is made to be carried out in a short period of time in a simple and stable way.
Variation of beam intensity of each laser beam including variation of beam intensity caused not only by variation of luminescence intensity of a laser beam with the passage of time but also by a change in an optical axis is made to be corrected satisfactorily.
The first object of the invention can be attained by the following structur.
An exposing apparatus comprises
a first laser beam source for being directly modulated in terms of light amount and for emitting a first laser beam having a first wavelength;
a second laser beam source for emitting a second laser beam having a second wavelength different from the first wavelength; and
an audio-optical modulation element for modulating the second laser beam in terms of light amount.
Furthermore, the first object of the invention can be attained by the following preferable structures in Items 1-9.
Item 1
A laser exposure unit wherein laser beams of at least two different wavelengths or more scan a recording medium to expose an image for formation thereof, wherein a laser beam which is modulated in terms of an amount of light by direct modulation and a laser beam which is modulated in terms of an amount of light by an audio-optical modulation element are combined to constitute the unit.
In the constitution mentioned above, image exposure is carried out by a combination of a laser beam which is subjected to direct modulation (internal modulation) and a laser beam which is subjected to external modulation by an audio-optical modulation element (AOM).
Item 2
The laser exposure unit wherein the laser beam which is modulated in terms of an amount of light by the direct modulation is a semiconductor laser and the laser beam which is modulated in terms of an amount of light by the audio-optical modulation element is a gas laser or a solid laser.
In the constitution mentioned above, with regard to the semiconductor laser, light amount modulation corresponding to image signals is carried out by ON and OFF of an electric current which flows through the semiconductor laser, and with regard to output of the gas laser or the solid laser, light amount modulation corresponding to image signals is carried out by the audio-optical modulation element (AOM). As the gas laser mentioned above, it is preferable to use a Hexe2x80x94Ne laser, while as the solid laser, it is preferable to use a laser diode (LD) exciting solid laser. Further, it is preferable to employ the structure wherein one of CMY light-sensitive layers is made to a light-sensitive material sensitive to infrared light as a recording medium, and a gas laser or a solid laser is used as a short wavelength light source (G light source) by shifting the light source toward infrared, and a semiconductor laser is used as a light source (R and infrared light source) with two wavelengths other than the aforesaid short wavelength.
Item 3
The laser exposure unit provided with a beam forming optical means which causes a beam form of the semiconductor laser which is modulated in terms of an amount of light by the direct modulation to agree with a beam form of the gas laser or the solid laser which is modulated in terms of an amount of light by the audio-optical modulation element
Since a beam form of a gas laser or a solid laser is completely round while that of a semiconductor laser is elliptical generally, a beam form of a semiconductor laser is made to be completely round so that a beam form of each wave may be the same as others.
Item 4
The laser exposure unit wherein there are provided an incident beam diameter reducing means which reduces a diameter of a laser beam entering the audio-optical modulation element and a beam diameter restoring means which restores a diameter of a laser beam emitted from the audio-optical modulation element reduced by the incident beam diameter reducing means to its original diameter.
Since the response speed in the audio-optical modulation element (AOM) is dependent on the beam diameter, a diameter of a laser beam is reduced to improve the response speed before it enters AOM and then the laser beam is caused to enter AOM to be modulated therein, and after that the diameter of the laser beam is restored.
Item 5
The laser exposure unit wherein there is provided an exposure timing adjustment means which synchronizes exposure timing between the laser beam modulated directly and the laser beam modulated in terms of an amount of light by the audio-optical modulation element.
In the aforesaid structure, the means to synchronize exposure timing is provided because a delay is caused in modulation made by AOM compared with direct modulation of a laser beam. To be concrete, it is possible to synchronize exposure timing by shifting a beam position by an amount of the delay stated above, or by delaying modulation data for the direct modulation by an amount of the delay of AOM.
Item 6
The laser exposure unit wherein there is provided a reducing optical means which reduces the laser beam to the desired beam diameter and projects a beam of the reduced diameter on the recording medium as a collimated beam.
In the aforesaid structure, when scanning a recording medium for exposure by reducing a diameter, a collimated beam with the reduced diameter, namely the beam whose diameter does not change regardless of the distance from a lens, is projected on the recording medium.
Item 7
The laser exposure unit structured so that a recording medium is scanned for exposure by plural laser beams for each wavelength and plural laser beams are modulated simultaneously by the audio-optical modulation element, wherein there is provided a pitch changing means which makes an internal of a laser beam modulated in terms of an amount of light by the direct modulation to agree with that of a laser beam in the audio-optical modulation element.
In the aforesaid structure, an interval of a laser beam modulated directly is changed so that the internal of a laser beam modulated directly may agree with that of plural laser beams modulated simultaneously by the audio-optical modulation element, under the structure that a recording medium is scanned for exposure by plural laser beams for each wavelength and plural laser beams are modulated simultaneously by the audio-optical modulation element.
Item 8
The laser exposure unit wherein there is provided a pitch reducing means which reduces plural laser beams adjusted in terms of a beam interval by the pitch changing means and modulated in terms of an amount of light by the direct modulation and plural laser beams modulated in terms of an amount of light by the audio-optical modulation element to the same pitch simultaneously.
In the aforesaid structure, laser beams modulated by the audio-optical modulation element (AOM) and laser beams modulated directly both of which are changed to be of the same beam interval are collectively reduced to the same pitch and are caused to scan a recording medium for exposure.
Item 9
The laser exposure unit structured so that the number of mirrors interposed in an optical path of a laser beam with a longer wavelength is less than that of mirrors interposed in an optical path of a laser beam with a shorter wavelength.
In the aforesaid structure, in the case of a laser beam having a longer wavelength, a recording medium is exposed to light through less mirrors compared with the occasion of other laser beams having shorter wavelengths. The mirrors mentioned above are optical mirrors which require assembling and adjustment, and laser beams having a longer wavelength require less mirrors requiring the assembling and adjustment than other laser beams having a shorter wavelength do. For example, when using an infrared wavelength as a long wavelength, the laser beams having an infrared wavelength which are hard to see require less mirrors which require adjustment.
The structures of Items 1 and 2 offer an effect that it is possible to avoid a light source which is large in size and high in cost and to use a recording medium (light-sensitive material) which is easily manufactured and preserved and is low in cost, by using a laser beam modulated directly and a laser beam modulated in terms of an amount of light by an audio-optical modulation element in combination.
The structure of Item 3 offers an effect that a difference of a beam form between a semiconductor laser and a gas laser or between a semiconductor laser and a solid laser can be corrected and all beams are made to be the same in a form to be caused to scan for exposure.
The structure of Item 4 offers an effect that it is possible to improve a response of an audio-optical modulation element by reducing a diameter of a beam entering the audio-optical modulation element.
The structure of Item 5 offers an effect that it is possible to scan for exposure by synchronizing exposure timing even if there is a delay in modulation in terms of an amount of light made by an audio-optical modulation element for the laser beam modulated directly.
The structure of Item 6 offers an effect that it is possible to scan for exposure with a constant beam diameter even when a distance from a recording surface to an optical head varies, by projecting a laser beam on a recording medium as a collimated beam.
The structure of Item 7 offers an effect that a precision of superposition of each wavelength is improved when an interval of a laser beam modulated directly is made to be the same as that of a beam in the audio-optical modulation element in the structure where the audio-optical modulation element which modulates plural laser beams simultaneously is used.
The structure of Item 8 offers an effect that resolution and the number of lines can easily be changed because intervals of beams for various wavelengths are made to be the same in advance as stated above and they are reduced collectively.
The structure of Item 9 offers an effect that it is possible to reduce the number of optical mirrors requiring adjustment related to a laser beam having the wavelength that is hard to see, and thereby to assemble and adjust easily.
The second object of the invention can be attained by the following preferable structures of Items 10-20.
Item 10
An image recording apparatus having therein a light source section wherein plural laser diodes are arranged, a beam arranging optical system which arranges laser beams emitted from the plural laser diodes on the recording surface of a recording material in the sub-scanning direction, a moving means which moves the laser beams emitted from the plural laser diodes and the recording material relatively in the main scanning direction, a measuring means which measures beam intensity of each of the laser beams emitted from the plural laser diodes, and a laser diode control means which controls each of the plural laser diodes so that beam intensity of each laser beam may become the same as others, in accordance with beam intensity of each laser beam measured by the measuring means stated above, wherein a filter adjustment means which shifts with a filter the exposure intensity of all laser beams emitted from the plural laser diodes.
In the structure of Item 10, occasional making all laser beams to be of the same intensity is conducted by controlling an electric current which flows through each of plural laser diodes, which results in accurate adjustment, while frequent shifting of beam intensity of all laser beams emitted from plural laser diodes is conducted by a filter, which results in simple adjustment.
Item 11
The image recording apparatus stated above wherein the filter adjustment means shifts exposure intensity of all laser beams emitted from the plural laser diodes when plural filters each having different density are selectively interposed in or removed from an optical path of a laser beam.
In the structure of Item 11, frequent shifting of beam intensity of all laser beams emitted from plural laser diodes can be conducted on plural steps.
Item 12
The image recording apparatus stated above wherein the filter adjustment means has an optical wedge filter, and exposure intensity of all laser beams emitted from the plural laser diodes can be shifted by changing a beam incident position on the optical wedge filter.
In the structure of Item 12, the filter adjustment means which is small in size and simple in structure makes it possible to conduct frequent shifting of beam intensity of all laser beams emitted from plural laser diodes on plural steps or continuously.
Item 13
The image recording apparatus stated above wherein the optical wedge filter is a disk-shaped optical wedge filter, and laser beams emitted from the plural laser diodes are caused to enter the disk-shaped optical wedge filter so that a beam incident position on the disk-shaped optical wedge filter may be in the direction of the same radius of the disk-shaped optical wedge filter.
In the structure of Item 13, beam intensity of each of laser beams emitted from plural laser diodes can be shifted by the same amount accurately.
Item 14
The image recording apparatus stated above wherein there is provided a beam converging means which converges incident positions on the aforesaid filter for all laser beams emitted from the plural laser diodes mostly to one point.
In the structure of Item 14, degree of freedom for the positional relation between a laser beam and a filter is increased, and lack of uniformity of a filter does not affect, whereby beam intensity in each of laser beams emitted from plural laser diodes can be shifted by the same amount accurately even when a filter which varies its density depending on its position like an optical wedge filter is used.
Item 15
An image recording apparatus having therein a light source section wherein plural laser diodes are arranged, a beam arranging optical system which arranges laser beams emitted from the plural laser diodes on the recording surface of a recording material in the sub-scanning direction, a moving means which moves the laser beams emitted from the plural laser diodes and the recording material relatively in the main scanning direction, a measuring means which measures beam intensity of each of the laser beams emitted from the plural laser diodes, and a laser diode control means which controls each of the plural laser diodes so that beam intensity of each laser beam may become the same as others, in accordance with beam intensity of each laser beam measured by the measuring means stated above, wherein a polarizer adjustment means which shifts with a polarizer the exposure intensity of all laser beams emitted from the plural laser diodes is provided.
In the structure of Item 15, occasional making all laser beams to be of the same intensity is conducted by controlling an electric current which flows through each of plural laser diodes, which results in accurate adjustment, while frequent shifting of beam intensity of all laser beams emitted from plural laser diodes is conducted by a polarizer, which results in simple adjustment.
Item 16
The image recording apparatus stated above wherein there is provided a beam converging means which converges incident positions on the aforesaid polarizer for all laser beams emitted from the plural laser diodes mostly to one point.
In the structure of Item 16, degree of freedom for the positional relation between a laser beam and a polarizer is increased, and lack of uniformity of a polarizer does not affect, whereby beam intensity in each of laser beams emitted from plural laser diodes can be shifted by the same amount accurately.
Item 17
An image recording apparatus having therein a light source section wherein plural laser diodes are arranged, a beam lining up optical system which lines up laser beams emitted from the plural laser diodes on the recording surface of a recording material in the sub-scanning direction, a moving means which moves the laser beams emitted from the plural laser diodes and the recording material relatively in the main scanning direction, a measuring means which measures beam intensity of each of the laser beams emitted from the plural laser diodes, and a laser diode control means which controls each of the plural laser diodes in accordance with beam intensity of each laser beam measured by the measuring means stated above, wherein a photoreceptor element capable of moving relatively to the position where a laser beam emerging from the beam lining up optical system can be received receives each laser beam emitted from each of the plural laser diodes and emerging from the beam lining up optical system, whereby the measuring means measures beam intensity of each laser beam emitted from each of the plural laser diodes.
In the structure of Item 17, variation of beam intensity of each laser beam including variation of beam intensity caused not only by variation of luminescence intensity of a laser beam with the passage of time but also by a change in an optical axis is made to be corrected satisfactorily.
Item 18
The image recording apparatus stated above wherein the photoreceptor element is made to be movable relatively to a recording surface of the recording material on which the laser beam records.
In the structure of Item 18, beam intensity of each laser beam on the recording surface of the recording material can be detected directly, and thereby variation of the beam intensity of each laser beam can well be corrected.
Item 19
An image recording apparatus having therein a light source section wherein plural laser diodes are lined up, a beam arranging optical system which lines up laser beams emitted from the plural laser diodes on the recording surface of a recording material in the sub-scanning direction, and a moving means which moves the laser beams emitted from the plural laser diodes and the recording material relatively in the main scanning direction, wherein a luminescence timing control means which delays luminescence timing of each laser diode of the plural laser diodes individually is provided.
In the structure of Item 19, it is possible to delay luminescence timing of each laser diode individually even when a precision of mounting each laser diode is not so high as a recording position of each laser beam of the plural laser diodes on the recording surface of a recording material shifts in the sub-scanning direction. Therefore, it is possible to correct properly the effect of deviation of the recording position of a laser beam emitted from each laser diode in the main scanning direction resulted from deviation of an optical axis caused by environmental conditions or the passage of time, and it is possible to record satisfactorily.
Item 20
The image recording apparatus having therein a recording position detector which can move relatively to the recording surface of the recording material for the laser beam and detects the recording position for each laser beam emitted from the plural laser diodes, wherein the luminescence timing control means delays luminescence timing of each laser diode individually for each laser diode of the plural laser diodes in accordance with the recording position of a laser beam emitted from each laser diode detected by the recording position detector.
In the structure of Item 20, a recording position of a laser beam emitted from each laser diode is automatically measured, and an amount of delay of luminescence timing of each laser diode is determined and controlled in accordance with the measured recording position of the laser beam emitted from each laser diode. Therefore, an effect of the deviation of the recording position of the laser beam emitted from each laser diode in the main scanning direction resulted from deviation of an optical axis caused by environmental conditions and the passage of time can properly be corrected automatically, and thereby less time is required for maintaining quality of recorded images, resulting in satisfactory recording.